The invention relates to memory allocation and more particularly to memory allocation in a multithreaded (parallel) environment.
In allocating memory for a computer program, most older languages (e.g., FORTRAN, COBOL) require that the size of an array or data item be declared before the program is compiled. Moreover, the size of the array or data item could not be exceeded unless the program was changed and recompiled. Today, however, most modern programming languages, including C and C.sup.++, allow the user to request memory blocks from the system memory at run-time and release the blocks back to the system memory when the program no longer needs the blocks. For example, in these modern languages, data elements often have a data structure with a field containing a pointer to a next data element. A number of data elements may be allocated, at run-time, in a linked list or an array structure.
The C programming language provides memory management capability with a set of library functions known as "memory allocation" routines. The most basic memory allocation function is called malloc which allocates a requested number of bytes and returns a pointer that is the starting address of the memory allocated. Another function known as free returns the memory previously allocated by malloc so that it can be allocated again for use by other routines.
In applications in which memory allocation occurs in parallel, for example, in a multithreaded process, the malloc and free functions must be "code-locked". Code-locking means that the library code of the process containing the thread is protected with a global lock. This prevents data corruption in the event that one thread is modifying a global structure when another thread is trying to read it. Code-locking allows only one thread to call any of the malloc functions (e.g., malloc, free, realloc) at any given time with other threads waiting until the thread is finished with its memory allocation. Thus, in a multithreaded process in which memory allocation functions are used extensively, the speed of the system is seriously compromised.